I have had this problem since I brought my 1985 300D a few months ago.

When the car hits 45 I get a strange vibration in the rear of the car. Well the tires on the car were ten years old so I replaced them and everything balanced out perfect.

Well I still have the same vibration starting at 45mph until 55-60mph.
I brought a new flex disc but I have not had time to install.

Any other ideas??

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On the hunt...
1985 300D----Sold
1985 300TD---Sold
1983 300SD---Sold

Flex disc and check the rear end fluid as well. As with any second hand car, never assume.

I will try and get the flex disc on this weekend and report back

Thanks

__________________
On the hunt...
1985 300D----Sold
1985 300TD---Sold
1983 300SD---Sold

Don't eliminate the front end. Vibrations are such low frequency they are difficult to directionally isolate. I would look at the front bearings. Take the weight off the tire and check by trying to wiggle top to bottom of the wheel. Side to side checks tie rod ends.

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1999 Mercedes E300TD daily driver sold at 238K miles 106K miles were mine, rust worm got it :-(
2006 Mercedes CDI new daily driver! 56,000 miles May 2016 now 85,625 Apr 2018 and Apr 2019 101,000 miles Apr 2020 109,875. March 2024 135,250, Dec 2024 145,000 miles